At the 2015 climate summit in Paris, negotiators adopted 2 °C as the upper limit for global warming, with a view to limiting it to 1.5 °C. I suggest that more research is needed into ecosystems that are highly sensitive to temperature shifts and that deliver multiple ecosystem services, such as mountains and corals. Such work could help in the assessment of these targets and of the risks associated with climate-mitigation options such as bioenergy and geoengineering.
The Intergovernmental Panel on Climate Change is moving forward with its special report on the 1.5 °C warming and its Sixth Assessment Report. Each document will need to consider the future impacts of the two targets on biodiversity, ecosystems and humans — and what it would take to achieve the 1.5 °C target.
In the Himalayas, for example, projected mean increases of 1.8 °C, 2.2 °C and 3.7 °C in global mean surface temperatures for 2081–2100 (relative to 1986–2005) would lead to significantly greater loss of glaciers than if the projected increase is 1.5 °C or less (P. D. A. Kraaijenbrink et al. Nature 549, 257–260; 2017). These glacier changes would affect biodiversity and human populations by altering species distributions, water regimes, farming and the risks of outburst floods from glacier lakes.
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